For the production of oil from oil shale using radio frequency heating, the tubing in the RF field must be non-metallic, such as ceramic, and capable of high temperatures (400.degree. C.+). Heating must be such that the oil shale temperature is maintained near, but not over, a maximum fixed value.
To permit the temperature measurements, a thermal well must be maintained through the heated zone. However, because of thermal expansion due to operating at these high temperatures, thermal expansion often causes thermal well tubing (ceramic) cracking and breaking. When this happens it becomes necessary to set a bridge plug near the broken section to prevent produced gases from flowing up the tube.
The materials of the bridge plug must be able to withstand the high operating temperatures and thus cannot be any of the elastomers.
This invention also includes a new method for fishing cylindrical objects from deep in a well.
Fishing is the operation to recover from a wellbore any equipment accidentally left there during drilling operations. Also it is the operation to remove certain items of equipment from an older well in order that the well may be reconditioned. In a well being drilled, the most common fishing operation is that required by the loss of a drill bit, one or more drill collars, or a part of the string of drill pipe. Additional items often fished from wells are packers, liners, screen pipe, etc. It may be noted that a great majority of these items are cylindrical. Thus to retrieve these items from deep in a well, a good, reliable, foolproof, and simple fishing tool is highly desired.